A variety of sophisticated, measuring systems have been developed in the prior art. For example, time domain reflection techniques have been applied to radar and sonar. Light wave interferometry has also been used for such things as measuring the wave length of light and measuring the density differences at various points in a supersonic wind tunnel. Standing interference fringes have also been described involving sound waves or the vibration of a physical mass.
These techniques, however, involve standing interference fringes. That is, the interference fringes are in a fixed spatial position determined by the frequency and phase of the radiated waves and the positioning of the radiators relative to each other and relative to the surface upon which the interference fringes are observed.
One particular application of travelling wave interferometry techniques is in a solar power satellite system. Such a system has a large number of solar power transducers, which convert solar light energy to electrical energy, mounted on the solar power satellite. These solar power transducers are connected to microwave oscillator circuits which in turn are connected to radiating antennas mounted on the solar power satellite. The solar power satellite has a plurality of antennas arranged in a suitable antenna array, each antenna or subarray radiating a portion of the total power. In this manner solar energy can be converted to microwave electrical energy and radiated as electromagnetic waves to earth as a composite beam.
On earth an antenna field comprising an array of receiving antennas will receive the microwave energy. The energy of the microwave beam is then converted to useful DC and/or another electrical energy form.
In order to have efficient coupling of energy from the solar power satellite to earth, it is desirable that the waves radiated from each separate radiating antenna or radiator of the space antenna impinge upon the receiving antenna array as nearly in phase as possible. By arriving in phase they will, at the receiving antenna field, produce the reinforcing effect of constructive interference also termed constructive reinforcement rather than the cancelling effect of destructive interference. It is therefore desirable that the waves from all the individual antennas on the space antenna arrive at the receiving antenna on earth in the form of a planar wave front.
It is desirable, but not necessary, to form the planar wave front about a reference antenna on earth which is located at the center of the receiving antenna array.
In order to create such a planar wave front, the phase of the wave radiated from each space antenna or subarray must be properly phased so that all waves arrive in phase. Phase corrections for each radiating space antenna are therefore necessary to correct the phasing of the wave from each antenna. The phase corrections electrically point or steer the radiated beam and also compensate for phase variations within the electrical circuitry of the solar power satellite as well as variations in the physical positioning of the individual antennas in the antenna array of the solar power satellite.
One suggestion for compensating the phase of each antenna is that a pilot signal be transmitted from the receiving antenna site on earth. The pilot signal would be received by retrodirective arrays on the solar powered satellite which phase conjugate the pilot signal so that the net phase shift of the transmitted signal from each individual antenna as observed in the plane of the power beam wave front is zero. However, it is believed that ionospheric effects preclude the use of a pilot beam from earth for accurate phase compensation.
It is therefore desirable and an object of the invention to phase compensate the space antenna with a system which is not subject to those effects and which has a considerably wider scope of useful application.